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GeezerVison is showing github.com — gh-115035: Mark ThreadHandles as non-joinable earlier after forking by colesbury · Pull Request #115042 · python/cpython

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@colesbury

@colesbury colesbury commented Feb 5, 2024 •
edited by bedevere-app Bot
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This marks dead ThreadHandles as non-joinable earlier in PyOS_AfterFork_Child() before we execute any Python code. The handles are stored in a global linked list in _PyRuntimeState because fork() affects the entire process.

  • Issue: Crash in ThreadHandle_dealloc after fork in free-threaded build #115035

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@colesbury
pythongh-115035: Mark ThreadHandles as non-joinable earlier
8130173 
This marks dead ThreadHandles as non-joinable earlier in
`PyOS_AfterFork_Child()` before we execute any Python code. The handles
are stored in a global linked list in `_PyRuntimeState` because `fork()`
affects the entire process.
@colesbury
colesbury requested review from ericsnowcurrently, gpshead and pitrou February 5, 2024 22:22
@bedevere-app bedevere-app Bot added the awaiting review label Feb 5, 2024
@bedevere-app bedevere-app Bot mentioned this pull request Feb 5, 2024
Crash in ThreadHandle_dealloc after fork in free-threaded build #115035
Closed
@colesbury colesbury added the skip news label Feb 5, 2024
@colesbury colesbury changed the title gh-115035: Mark ThreadHandles as non-joinable earlier gh-115035: Mark ThreadHandles as non-joinable earlier after forking Feb 5, 2024
@colesbury

colesbury commented Feb 5, 2024

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This doesn't call PyThread_update_thread_after_fork(). As far as I can tell, that call did not have any effect: we determine the current thread using PyThread_get_thread_ident_ex() (via get_ident) 1 so there's no way we could have a thread with a stale identifier. And if we don't find a matching thread, we create a new _MainThread() with the correct current identifier (and no handle).

Footnotes

  1. https://github.com/python/cpython/blob/c32bae52904723d99e1f98e2ef54570268d86467/Lib/threading.py#L1725-L1731 ↩
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@pitrou

pitrou commented Feb 6, 2024

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As far as I can tell, that call did not have any effect: we determine the current thread using PyThread_get_thread_ident_ex() (via get_ident) 1 so there's no way we could have a thread with a stale identifier.

That's a good point, but then we can probably remove the PyThread_update_thread_after_fork function?
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pitrou
pitrou reviewed Feb 6, 2024
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Comment thread Include/internal/pycore_pythread.h Resolved

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Comment thread Modules/_threadmodule.c Resolved

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@colesbury
Add comment and remove unused code.
5b8c1c1
@colesbury
colesbury requested a review from pitrou February 6, 2024 15:51
pitrou
pitrou approved these changes Feb 6, 2024
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Neat, thank you @colesbury !

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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting review labels Feb 6, 2024
@pitrou

pitrou commented Feb 6, 2024

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Note: you're a core developer now ;-)
colesbury and itamaro reacted with hooray emoji
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@colesbury
colesbury merged commit b6228b5 into python:main Feb 6, 2024
@bedevere-app bedevere-app Bot removed the awaiting merge label Feb 6, 2024
@colesbury
colesbury deleted the gh-115035-thread-handle branch February 6, 2024 19:45
@gpshead

gpshead commented Feb 7, 2024

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nice refactoring, thanks! happy first-ish merge!
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fsc-eriker pushed a commit to fsc-eriker/cpython that referenced this pull request Feb 14, 2024
@colesbury @fsc-eriker
pythongh-115035: Mark ThreadHandles as non-joinable earlier after for…
dffd892 
…king (python#115042)

This marks dead ThreadHandles as non-joinable earlier in
`PyOS_AfterFork_Child()` before we execute any Python code. The handles
are stored in a global linked list in `_PyRuntimeState` because `fork()`
affects the entire process.
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Reviewers

@pitrou pitrou pitrou approved these changes
@gpshead gpshead Awaiting requested review from gpshead
@ericsnowcurrently ericsnowcurrently Awaiting requested review from ericsnowcurrently ericsnowcurrently is a code owner

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3 participants

@colesbury @pitrou @gpshead
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